Optical graduated rule of transparent material

ABSTRACT

Transparent material having internal reflection properties is used to fabricate a graduated optical rule usable in tachometer or displacement measuring systems. The member has a lightreceiving surface through which light is transmitted toward a remote surface in a given direction. Such remote surface has alternating first surface portions respectively having a 45* angle with respect to said given direction and, preferably, second surface portions that are perpendicular to said given direction. The 45* surface portions reflect the light to a first light path, while the second surface portions permit the light to be transmitted therethrough along a second light path. Facing ones of said first or 45* angled portions are utilized to reflect the light through such first light path which intersects the light receiving surface back toward the light source. In another embodiment, light enters the member at 45* through a light receiving surface. A continuous internal surface disposed at 45* with respect to the light-receiving surface reflects light toward the remote surface in such given direction. The remote surface has the first and second surface portions disposed with respect to light traveling in such given direction reflected from the internal surface for alternately reflecting and transmitting through the remote surface toward a detector. Several utilization arrangements are illustrated.

United States Patent [72] Inventor Gene A. Fisher Boulder, C010. [21]Appl. No. 837.826 [22] Filed June 30, 1969 [45] Patented Aug. 10, 1971[73] Assignee International Business Machines Corporation Armonk, N.Y.

[54] OPTICAL GRADUATED RULE OF TRANSPARENT MATERIAL 15 Claims, 12Drawing Figs.

[52] [1.8. CI 356/152, 350/1 12, 350/285, 250/231 [51] 1nt.C1 ..G02b17/00 [50] Field of Search 350/99, 103, 273, 285, 109,12, 266; 356/152;73/488; 324/175; 33/129; 250/233, 231 SE [56] References Cited UNITEDSTATES PATENTS 2,818,500 12/1953 Franck 350/103 3,524,067 8/1970 West250/231 R FOREXGN PATENTS 991,873 5/1965 Great Britain 350/112 SECONDLIGHT PATH Primary Examiner- Rodney D. Bennett, .lr. AssirranlExaminer-S. C. Buczinski Attorneys-Hanifin and Jancin and Herbert F.Somermeyer ABSTRACT: Transparent material having internal reflectionproperties is used to fabricatea graduated optical rule usable intachometer or displacement measuring systems. The member has alight-receiving surface through which light is transmitted toward aremote surface in a given direction. Such remote surface has alternatingfirst surface portions respectively having a 45 angle with respect tosaid given direction and, preferably, second surface portions that areperpendicular to said given direction. The 45 surface portions reflectthe light to a first light path, while the second surface portionspermit the light to be transmitted therethrough along a second lightpath. Facing ones of said first or 45 angled portions are utilized toreflect the light through such first light path which intersects thelight receiving surface back toward the light source. In anotherembodiment, light enters the member at 45 through a light receivingsurface. A continuous internal surface disposed at 45 with respect tothe light-receiving surface reflects light toward the remote surface insuch given direction. The remote surface has the first and secondsurface portions disposed with respect to light traveling in such givendirection reflected from the internal surface for alternately reflectingand transmitting through the remote surface toward a detector. Severalutilization arrangements are illustrated.

22 55 52 i W W FlRSl LIIGHT PAITH u RECEIVING sumcr ,21 115 66/ 55 M16 i20 20 H8 20 119 REMOTE SURFACE 55 H 50 117 PATENTEUAUGIOIHY! 3,598,493.

SHEET 1 [IF 2 35 32 55 2 V13 14 f22 35 53 52 53 32 %/A %//)%A V%/;AV///% W///% u T SECOND LIGHT PATH? PFIRST LIGHT PATH RECEIVING SURFAOE\l L l l l I I l r r I I r r f r 1 IIIIIII I 1/ 1,1, r l f// M60218)::g297oO326[1/{ ,21/ 9 1, 116 so 20' 20 20 20 52 +30"? 2 147 A W W W/% Ws1 s1 51 a4 51 DETECTOR FIG 4 58 f SOURCE s5 5 INVENTOR 95 9.2 4 '83 80ENE A. FISHER 1 f r L- v w 55/ W 1 f W J I g 86 as 89 81 f ATTORNEYBACKGROUND OF THE INVENTION The present invention relates to measurementdevices utilizing optical techniques and, more particularly, to agraduated rule constructed of wholly transparent material and systemsemploying such a graduated rule.

Optical measuring systems are finding wider and wider applications asdisplacement measurement devices, tachometers, and related devices. Manysuch optical systems selectively actuate photodetectors which generatepulsating electrical currents in response to such selective actuation.Selective actuation of photodetectors can provide alternate times oflight and no-light to which the photodetector is photoresponsive. Suchoptical systems can be generally categorized as refractive, reflective,or see-through. The reflective and seethrough optical systems are mosteasily operated with digital control systems in that the optical systemis easy to make digital in character. Such digitalization of an opticalsystem is usually accomplished by using reflective and nonreflectiveportions in a reflective system; opaque and transparent portions in asee-through type of system. Refraction systems can be used to create aphase shift in an electrical signal generated in response to refractedlight waves when compared with a standard. Also, such refraction systemshave been used to disperse light such that the light intensity suppliedto a light detector is switched between two light intensities.

of prime importance in a digitalized optical system is the socalledlight to dark ratio. Such ratio occurs in all three categories ofoptical systems. The greater the ratio, the more reliable the opticalsystem will tend to be. Also, in many operating environments, theoptical system may be subjected to an accumulation of particulate matterwhich interferes with the reflectivity, light transmissiveness, orrefraction of light by the optical system. Such particulate matter has atendency to reduce the above-mentioned light to dark ratio. Therefore,in many optical systems. if the light to dark ratio initially ismarginal; then, when that system is operated in an environment ofparticulate matter, the performance could become unsatisfactory.Therefore, it is desired in a digitalized optical system to have as highas possible light-to-dark ratio.

Some digitalized optical systems of the reflective or seethrough" havebeen fabricated using photolithographic techniques to form alternatereflective and nonreflective surfaces or opaque and transparentsurfaces. Photolithographic techniques are relatively expensiveresulting in a relatively expensive graduated rule. Photolithographictechniques, however, are satisfactory for creating a large number ofalternate surface portions of light and dark areas to a high degree ofaccuracy. It has been found that, even with so-called opaque coating orsurface on an optical rule, the light-to-dark ratio is not high. Thatis, in precise graduated rules, for example, of 100 of more alternateareas per inch, the so-called opaque area is not truly opaque (i.e.,allows some light to be transmitted). In the reflective systems, even inthe nonreflective areas, some light is reflected. A light-to-dark ratioof :1 is not unusual in a new graduated rule for use in a displacementmeasuring device. Such a light-to-dark ratio requires sensitiveelectrical circuits which add to the cost of making a completedisplacement measuring device and tends to reduce the fidelity and thereliability of the measurements being made.

Many digitalized optical measurement systems use graduated rules in theform of a disc or annulus mounted on a rotating member such as a motorshaft, pulley, and the like. Some of these systems are designed to behigh-acceleration devices requiring a low inertia rotor. Since eachtachometer disc or displacement measuring annulus has a finite weight,it adds to the inertia of the system and thereby has a tendency todegrade acceleration. In such high-acceleration systems, it is desirablethat the weight of the tachometer disc be minimized for minimizing theaddition to the inertia of the rotor. Even in such high accelerationsystems, cost is an overridin factor. The measurement disc, such as atachometer discf'sfiould be very precise, extremely lightweight, and,preferably, low cost and easily attachable to the rotating member.Further, because of production requirements in many areas, tachometerdiscs should be easily reproducible at a high rate with a minimum numberof fabrication steps to complete the optical graduated rule.

Many digitalized optical systems use a stationary mask having a smallaperture for limiting the area on the tachometer disc that affects thephotodetector. Such masks are usually required because the light sourceand detector have a broader light beam that the graduations on theoptical rule. To reduce the alignment problems inherent with the use ofa mask with a rotating disc or other movable optical graduated scale orrule, it is desired that the disc be designed to minimize the necessityfor a mask.

It is also desired to have an optical measuring rule of simple design,high resolution (high light/dark ratios) and easily and inexpensivelyreproducible.

SUMMARY OF THE INVENTION It is an object of this invention to provide adigital optical graduated rule of wholly transparent material and beingfabricatable using molding techniques.

It is a corollary object to the above object to provide an optical ruleof simple construction having very high light-to-dark ratios.

It is another object to provide an optical graduated rule of extreme lowcost.

The invention uses transparent material having internal reflectionproperties such as thermoplastic resins. Exemplary thermoplastic resinsinclude polycarbonates and acrylics. lntemal reflection properties arethose properties of transparent material to reflect light beingtransmitted within the material when such light impinges upon aninternal surface disposed at 45 with respect to the direction of lighttravel. The internal surface is backed by a relatively smooth externalsurface. The smoother the surface, the better the reflectivity. Acoating (such as aluminum) on such external surface may (and usuallydoes) reduce the reflectivity of the internal surface.

A graduated rule using the above material in accordance with theinvention receives light through a light-receiving surface and transmitssuch light within the material in a given direction toward a remotesurface. The remote surface has a first set of surface portions disposedsubstantially at 45 with respect to the given direction for reflecting,in accordance with the internal reflection properties, substantially alllight arriving along said given direction to a first set of light paths,respectively. The first light paths extend away from the firs surfaceportions inside the member at with respect to th' given direction andsuch that the first light paths do not intersect the remote surfaceportions. Preferably, the first light path returns through thelight-receiving surface such as to provide reflection of the lightimpinging upon the light-receiving surface. A second set of surfaceportions are interposed between adjacent ones of the first set ofsurface portions and disposed at other than 45 with respect to the givendirection for permitting light arriving along said given direction toleave the member of transparent material through the remote surface. Themember is thereby provided with alternate portions of light transmissiveareas and light reflective areas. Such'alternate portions are utilizableas digital indicia of displacement of the member. Light detectors can beplaced in either the first or second light paths for detectingdisplacement.

in one arrangement of the 45 or first set of surface portions, there arepairs of such portions facing each other inside the member such that helight arriving in a given direction at a first one of the first surfacesin the pair is reflected at 90 to said given direction to a second oneof said first surfaces in the pair. The reflected light in said firstpath arrives at the second one of said first set of surface portions tobe reflected toward the light-receiving surface in an antiparallelrelationship to and displaced from the received light. Therefore, thelight is reflected by the member of transparent material at a pointdisplaced from the point of receipt enabling a light source to shinelight at the member and a detector placed in side-by-side relationshipto receive such light. Such facing 45 surfaces may be separated byanother surface that is parallel to the light-receiving surface, or thetwo facing 45 surfaces may join to form a continuous opaque or lightreflective area. Many possible arrangements can be configured sing theteachings of the present invention, such as the disposition of acontinuous 45 disposed surface for reflecting the light from thelightreceiving surface toward the remote surface. The remote surface hasthe alternating first and second surface portions for respectivelyreflecting and transmitting light. The reflected light from the remotesurface is reflected to the 45 continuous surface and thence through thelight receiving surface. Other configurations are possible including aplurality of remote surfaces disposed such as to provide a plural phaselight transmission or light reflection. A single light transmissive anda pair of light reflective surfaces may be utilized to provide anoptical fiducial mark.

The present invention is utilizable not only in rotational displacementsystems but in rectilinear motion systems for providing accurate andeasily fabricated graduated optical scale systems for displacementmeasurement.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS For more clearly illustrating theinvention in all of the Figures, the illustrated 45 undulations aregreatly exaggerated from that expected in most practical implementationsof the invention.

FIG. 1 is an enlarged diagrammatic partial sectional view of an opticalgraduated rule used to illustrate the principles and teachings of thepresent invention.

FIG. 2 is an enlarged portion of FIG. 1 showing the effect of a slightlycurved surface joining a first surface portion disposed at 45 to a givendirection and a light transmissive or second surface portion disposed at90 with respect to a given direction along which light is transmitted.

FIG. 3 is a simplified low angle perspective view of a tubular motorarmature on which an annular tachometer disc is mounted utilizing theteachings of the present invention.

FIG. 4 is a diagrammatic and sectional view of an annular opticalgraduated rule including a continuous annular surface disposed at 45with respect to a light-receiving surface for reflecting light such thata remote surface and the light-receiving surface can be disposed on theouter periphery thereof.

FIG. 5 is a diagrammatic and sectional view of an annular graduated ruleof transparent material having a pair of continuous internallyreflective inner surfaces arranged to provide a source and detectorlight path at the outer periphery of the annular member.

FIG. 6 is a diagrammatic and sectional view of a platelike rotatablegraduated optical rule of the see-through type and utilizing theteachings of the present invention. Plural light paths are provided forplural graduated rules.

FIG. 7 is an enlarged partial-sectional view taken in the direction ofthe arrows along line 7-7 in FIG. 6 and illustrates the phase displacedrelationship of two graduated rules.

FIG. 8 is a diagrammatic and sectional view of an annular graduated rulehaving plural surfaces for reflecting light along a 90 path for enablinga light source and light detector to be disposed on the same axial sideof the member.

FIG. 9 is a diagrammatic and sectional view of an annular opticalgraduated rule using the teachings of FIG. 5 but having a different axisof rotation such that the light source and detector are on one axialside of the member rather than being disposed radially outwardly of themember as in FIG. 5.

FIG. 10 is a diagrammatic cross-sectional view of a platelike circulardisc having two independent light paths each with light receiving andremote surfaces while using the same reflective surface inside themember.

FIG. 11 is a partial diagrammatic sectional view of an optical graduatedscale utilizing the teachings of the present invention and showingcertain variations of reflective and light transmissive areas.

FIG. 12 is a partial diagrammatic showing of another embodiment in whichthe first and second surface portions of the remote surfaces arecoplanar, respectively.

DETAILED DESCRIPTION OF THE PREFERRED AND ILLUSTRATIVE EMBODIMENTS Theoperating principles of the present invention are explained withparticular reference to the preferred embodiment illustrated in FIG. 1.Member 10 consists wholly of transparent material having internalreflection properties. Examples are glasses and thermoplastic resins,such as polycarbonates and acrylics. Light-receiving surface I 1receives light, such as indicated by dotted lines 12, I3, and 14. Suchlight enters member 10 and is transmitted toward remote surface 15 in agiven direction again indicated by the respective dotted lines 12, 13,and 14. Remote surface 15 includes a set of first surface portions 20disposed at 45 with respect to such given direction. When lightrepresented by line 13 reaches a first surface portion 20, it isreflected by the internal reflection properties of member 10 along afirst light path having a first portion 21 extending at right angles tothe given direction. The first path portion 21 of the first light pathalso happens to extend parallel to light receiving surface I]. The firstpath portion 21 enables light to reach first surface portion 20' andthen be reflected in the direction indicated by dotted line 22. Theso-reflected light continues along the first light path through member10 thence through light-receiving surface back toward a light source(not shown). First light path 22, instead of intersectinglight-receiving surface I I, could be arranged to intersect anothersurface of member 10, such as an end or remote surface 15 at anotherarea. See FIG. 12 as an example. The reflected light along line 22 isdisplaced from the incident light represented by line 13 such that thefirst light path has a U-shape" to it. As will become apparent, thisarrangement permits a light source and a light detector disposed alongthe first light path to be placed on the same side of member 10 foroperating as an optical measurement device.

The first set of surface portions 20 are relatively smooth with noaluminization or other coating materials thereon. It has been found thatthe reflectivity of light reaching the set of first surface portions, asindicated by line 13, when smooth is almost percent reflected. Thisprovides a good light-todark ratio when the transmissive portions now tobe described efficiently transmit light.

Remote surface 15 also includes a set of second surface portions 30disposed at right angles to the given direction, as indicated by surfaceportions 30 and 30" with respect to lines 12 and 14, respectively. It isto be understood that the angle of disposition of the second set ofsurface portions 30 is not critical; that is, it need not be at rightangles to the given direction, but it can be at any angle substantiallynot 45". If the second set of surface portions are disposed other thanat right angles, the refraction properties of material constitutingmember 10 must be considered in the transmission of light through remotesurface 15.

Light reaching the set of second surface portions 30 from within member10, such as indicated by lines 12 and 14, is easily transmitted throughthose second set of surface portions, respectively, in second lightpaths. With the justdescribed arrangement using a polycarbonate, alight-to-dark ratio of about 100:1 was obtained when the first andsecond sets ofsurface portions were relatively clean and smooth.

Member 10 provides alternate areas of light transmission and lightreflection such that on the remote surface 15 side of the member thereare alternate areas of darkness and light as the member is moved withrespect to a fixed source or if a source is moved with respect to afixed member. The dark areas, which correspond to an opaque area on agraduated rule, are indicated by the hatched lines 31 and are coincidentwith the first set of surface portions 20. interposed between adjacentones of the dark areas are light areas in which light is transmittedthrough the respective ones of the second set of surface portions 30along the second light paths.

Light and dark areas also occur on the light receiving surface 11 sideof member 10. Those areas aligned with the first set of surface portionsreceive reflected light, such as along line 22, to provide a pluralityof light areas 32 in the first light paths, respectively. The second setof surface portions 30, by permitting light to be transmitted along thesecond paths through remote surface 15, provide dark areas 33 alonglight receiving surface 11, as represented by the hatching. Therefore,light provided from member 10 along first light paths provides lightareas on the light-receiving surface side, while light transmitted frommember 10 along the second light paths provides alternate light areas onthe remote surface side of member 10. In accordance therewith, theunitary optical graduated scale membbr 10, consisting wholly oftransparent material, can be used as a reflective rule, a see-throughrule, or a combination of both.

With respect to light arriving through light receiving surface 11 alongline 22, it should be observed such light arrives at first surfaceportion 20 from light receiving surface 11 and is reflected along lightpath portion 21 toward first surface portion 20". The light is thenreflected along line 13 toward light receiving surface 11. Thisrelationship gives rise to an interesting phenomena in detectingreflected light emitted from member 10 through light-receiving surface11. Assume that a light source is emitting light along line 13. Alsoassume that member 10 is moving to the left, as viewed in FIG. 1. Firstsurface 20" will first reflect light from the source (not shown)received along line 13. The first occurring first light path is alongline 22; that is, in the direction from which member 10 is moving towardthe light source. As member 10 continues to move, surface portion 20'then receives light from the justdescribed source; light is thenreflected downstream or in a direction of movement of member 10 and willbe returned through light-receiving surface 11 in a direction from suchlight source toward which member 10 is moving. If each and every lightarea 32 is to be detected, then either a pair of light detectors (notshown) disposed with respect to a light source therebetween, as willbecome apparent, are used; or, in the alternative, further reflectivesurfaces may be provided such that one light detector may be used. Ifonly a single light detector is used with no additional optics, thenlight areas 32, occurring at such single light detector, are equal toone-half the number of first surface portions 20.

An important factor in graduated rules used in optical measurementsystems is the abruptness between adjacent light and dark areas. Foraccurate detection and precise timing, as may be required in tachometersused with high-performance electric motors, there should be a sharpdemarcation between adjacent light and dark areas. This requirement isin addition to a good light-to-dark ratio between light and dark areas.In the fabrication of an optical graduated rule, such as shown in FIG.1, from a thermoplastic resin, the preferred and least expensive way offabrication is by molding the member. It is well known that in moldingplastics, it is difficult to obtain sharp corners, such as corners 35 inmember 10. The operation of the embodiments incorporating the presentinvention is not degraded in performance by a slight rounding of corners35. Such action is explained with respect to FIG. 2, which is anabbreviated enlarged sectional view at one corner 35 in member 10. Afirst surface portion 20 is disposed with respect to second surfaceportion at 45. Incident light being transmitted through member 10, inone instance, is represented by dotted line 36 and is reflected by firstsurface portion 20 in the direction of the arrow 36a. Actually, there isa small tolerance (i.e., the angle of the given direction with respectto first surface portion 20 may vary from exactly 45). This tolerance isshown in FIG. 2 by the angle 20 which may be on the order of 4;accordingly, surface 20 reflects light arriving at its surface at anangle from 43 through 47. Materials other than thermoplastic resins mayhave a different tolerance; also, different polycarbonates may havedifferent tolerances.

Assume for purposes of discussion, there is relative motion betweenmember 10 and the beam of incident light such that the light beam movessuccessively from line 36 to line 37 and thence to line 41. Whensuch=light is arriving along dotted line 37 in the given direction andimpinges remote surface 15 at the curvature of corner 35, instead ofbeing reflected, the light is refracted to follow path 38. If a lightdetector is in a position indicated by number 39 and is focused toreceive light along line 40, detector 39 sees none, or very little, ofthe refracted light. As relative motion between such light beam (line37) and member 10 continues, the refracted light beam 38 swings aroundin accordance with the curvature of corner 35. Such action, insofar aslight detection by a light detector is concerned, makes the cornerappear to be more abrupt than it actually is. Since such curvatures atcorners 35 can be made with small radii, it has been found that suchcurvatures inherent in molding operations have not been detrimental tothe resolution and the accuracy of optical graduated rules constructedin accordance with the teachings of the present invention. After therelative movement of member 10 and the light rat have moved past corner11, as indicated by dotted line 41, dt tector 42 (formerly representedby dotted box 39) then receives light transmitted through member 10. Theactual point on remote surface 15 at which time detector 42 firstreceives light from member 10 is approximately at point 43.

Good utilization of internal reflective properties requires asubstantially smooth surface on first surface portions 20. It is knownthat an optically smooth surface is considered any surface that hasundulations therein not greater than the wavelength of the light orother optical energy with which such a surface is to be used. Such asmooth surface is obtainable by so-called pitch polish techniques. Suchtechniques are well known and widely used. An optical member havingsmooth surfaces, in accordance with the teachings of the presentinvention, is preferably formed by injection molding a plastic member ina mold having relatively smooth surfaces. Actually, the surfaces of themold die parts need not be optically smooth when known injection moldingtechniques are used. The reason for this is that the material beinginjection molded sets or solidifies prior to filling very small toolmarking or other groove in a die part. As a result, the surface on thepart being injection molded has a smoother surface than such die parts.This phenomenon is easily demonstrated by using the same die part tocast mold a thermoplastic member and then use the same mold forinjection molding. Examinatir under a microscope will illustrate thedifference in smoothness of the two molded parts.

An injection-molded, optical graduated rule fabricated in accordancewith the teachings of the present invention may include microscopiclines or other deformations on the first set of surface portions 20 aswell as the other surfaces. If such deformations or undulations becomesubstantial (i.e., approach a wavelength of the light being used), theremay be a refraction of the light with a corresponding reduction inreflectivity of such first surface portions. In one fabricatedembodiment, such lines were easily visible using microscopic techniques.A light-to-dark ratio of about 60:] was still attained even with somesubstantial (used in terms of optical wavelength)undulations/deformations in the first surface portions.

As an example, protrusion 44, shown on first surface portion 20, istypical of a deformation resulting from a groove or mark in a die partin an injection molding operation. Such a deformation is relativelysmooth and will not transmit or refract a substantial amount of lighttherethrough. That is, a substantial portion of the light impinging upondeformation area 44 may still lie within the above-described tolerancesof reflectivity using the internal reflection properties of thematerial. If deformation 44 had a horizontal component (as viewed inFIG. 2) equal to one wavelength of the light (i.e., in the order ofmagnitude of 5 microinches, for example), light arriving along saidgiven direction will be transmitted therethrough toward a lightdetector, such as detector 42. Since these areas are relatively small,the amount of total light transmitted is usually quite small. Athreshold in a detector 42 can easily obviate the effects of such light.Accordingly, it is preferred that the internal reflecting surfaces be assmooth as possible in order to enhance the reflectivity thereof, andthereby increase the light-to-dark ratio to the maximum possible extent.It is appreciated, however, that cost factors in designing an opticalmeasuring rule in accordance with the present invention may overridesuch desired performance. Therefore, in low cost applications, firstsurface portions may have a substantial amount of irregularity and stillreflect sufficient light for a successful operation of such anembodiment. It is also permissible to coat the first surface portionsfor protecting same from environmentally caused changes, for example,scratching. It should be remembered that such coating reduces theoptical efficiency of the first surface portions. Such coating does notnecessarily destroy such internal reflection properties.

With more particular reference now to FIGS. 3-10 inclusive, severalillustrative applications of the invention, as described with respect toFIG. 1, to rotating members are described. It is understood, of course,that rectilinear motion or displacement can be measured as is apparentfrom inspection of FIG. 1. By appropriately forming the opticalgraduated rule, other forms of motion and displacement can be accuratelymeasured. For example, hyperbolic and parabolic displacements could bemeasured. Also, by varying the relative length of the first surfaceportions 20 and the second surface portions 30 in a graduated rule,address indicia may be provided. That is, a succession of first surfaceportions may have a length in accordance with a given permutation codeto represent a location address. Therefore, not only may the illustratedrule be used for making measurements, but it may also be usedsimultaneously for indicating a location address of a given measurement.It is to be understood that all of the now-described optical graduatedrules, discs, or members consist of transparent material exhibitinginternal reflection properties.

With particular reference now to FIG. 3, a tachometer application of thepresent invention is illustrated. Tubular armature 50 of a motor (notshown) is the rotating member thereof and is used to securely supportannular tachometer member 51 at one end thereof. Tachometer member 51,consisting of transparent materials, is inserted inside tubular annature50 for minimizing the addition of inertia to the armature. The weight ofmember 51, when made of thermoplastic, is less than a comparable memberfabricated from glass. Tachometer member 51 is constructed in accordancewith the teachings of the present invention having an annular-shapedlight-receiving surface 52 disposed opposite light source 53 and a pairof detectors 54 and 55. Remote surface 56 is formed on the inner annularperiphery of member 51 and has a set of first surface portions 57 and aset of second surface portions 58. Light from source 53, represented bydotted line 60, passes through light-receiving surface 52 on a radius ofmember 51. In accordance therewith, first surface portions 57 are formedto be at 45 with respect to a radius intersecting the midpoint of suchfirst surface portions. Second surface portions 58 are formedconcentrically with the light-receiving surface 52. As showndiagrammatically in FIG. 3, light along line 60 is reflected by one ofsaid first surface portions toward another one of said first surfaceportions then radially outwardly to detector 55, as explained previouslywith respect to FIG. 1. As member 51 is rotated with respect to lightsource 53, successive ones of first surface portions 57 reflect lightsuch that detectors 54 and 55 alternately receive reflected light. Inthe just-described arrangement, it is apparent that both the lightsource and light detectors are on the outer side of annular member 51serving as a graduated optical rule for use as a tachometer member.Alternately, light detector 61 may be secured on the inner portion ofmember 51 for sensing light passing through second surface portions 58.For simplicity, electrical connections to light source 53 and to lightdetectors 54, 55, and 61 are not shown. The output signals from suchlight detectors are supplied to suitable analysis and signal processingcircuits (not shown) for determining the rotational velocity of tubulararmature 50 in a known manner. Of course, the illustrated arrangementmay be used to measure angular displacements as well.

Another facile arrangement for a tachometer application is shown in FIG.3, wherein the disposition of light source 62 and light detector 63 ison a common diameter but on opposite sides of annular graduated rule 51.Light from source 62 passes through light receiving surface 52, thenceremote surface second surface portion 58a, through the center space ofmember 51, thence enters such member through second surface potion 58band radially outwardly through light-receiving surface 52 to lightdetector 63. The just-described light path is the second light path.Light detector 63 receives no light from light source 62 whenever lighttherefrom is reflected by first surface portions 57 into a first lightpath, returning toward source 62 in the same manner as explained forlight source 53. In the just-described arrangement, both light pathsultimately leave graduated rule member 51 from light-receiving surface52, but on diametrically opposite sides thereof.

Also shown in FIG. 3 is the usage of plural independent opticalmeasurement systems with one graduated rule.

In FIG. 4, annular member 65 has a large inner peripheral surface whichmay be secured to a tubular armature, such as shown in FIG. 3.Alternately, one of the radially extending surfaces 66 or 67 may besecured to a rotating member. In case of a rotating shaft, radial armsmay be formed on the shaft attached to the axial ends of the innersurface, such as at 68 or 69 or both. It is desired to keep suchattachments away from the center axial portion 70 in order to maintainthe internal reflectivity of inner annular surface at 70, as will becomeap parent. Member 65 has an annular continuous light-receiving surface71 disposed at 45 with respect to axis of rotation 72. Light istransmitted through the member to be reflected in a given direction bysurface portion 70, as indicated by dotted line 73. Inner annularsurface portion 70 is a reflection surface such that the given directionof the light approaching remote surface 74 is at right angles to theincident light supplied from source 75. As such, surface portion 70 isoptically intermediate light-receiving surface 71 and remote surface 74.Remote surface 74 is shaped as illustrated in FIG. 1 and selectivelytransmits to detector 76 through its respective second surface portionsalong second light path 77. The fist light path of remote surface 74retraces the incident light along dotted line 73 and is returned towardsource 75. Of course, a pair of detectors may be disposed injuxtaposition to light source 75, such as shown for light detectors 54and 55 in FIG. 3. The justdescribed arrangement permits both thedetector and the source to be disposed along the outer periphery oftransparent member 65.

FIG. 5 illustrates another version of a graduated rule in which lightsource 80 and light detector 81 are disposed at the outer periphery ofannular optical rule or member 82. Light from source 80 is transmittedalong dotted line 84 through light-receiving surface 83 to a firstcontinuous annular internal reflecting surface 85 disposed at 45 withrespect to dotted line 84. Light is then transmitted along dotted line87 axially to second continuous annular internal reflecting surface 86.Surface 86 reflects light from line 87 along a given direction indicatedby dotted line 88 to remote surface 89. Second light paths of remotesurface 89 are collectively indicated by dotted line 90 and lighttherein is detected by detector 81. Remote surface 89 is constructed asillustrated in FIG. 1. Both annular internal reflecting surfaces 85 and86 are optically intermediate light-receiving surface 83 and remotesurface 89.

The FIG. illustrated tachometer member may also be used for measuringangular displacement. Light receiving surface 83 and remote surface 89are on the same outer peripheral surface of member 82. It is somewhateasier to mount the FIG. 5 illustrated member on a shaft than the FIG. 4illustrated member. A small diameter shaft may be inserted in the innerannulus of member 82 with radial arms or a radial web being disposed andfixedly secured to the inner surface 91 without interfering with theoptical properties of member 82. Alternately, member 82 may be mountedon axial end surfaces 93 or 94 without affecting the optical propertiesof the member with respect to source 80 and detector 81. The first lightpaths of the member 82 are from remote surface 89 along dotted line 88to annular reflecting surface 85, then turns the first light path alongline 34 back toward source 80.

Referring next to FIG. 6 and 7, a platelike or disc-shaped rotatablemember 100 is shown providing two-phase optical signals. Member or disc100 is fixedly secured to rotating shaft 101 for rotation therewith. Theillustrated disc is used as a seethrough type but, as explained above,may be used as a reflective type. A pair of light sources 102 aredisposed at the outer periphery of disc 100 on one axial side thereofwith a corresponding pair of light detectors 103 disposed on the0pposite axial side thereof for receiving light selectively through disc100. Utilization means 104 receives the two-phase signal in electricalform from detectors 103. Disc 1110 has light receiving surface 105 fortransmitting light therethrough along dotted lines 106 in a givendirection. A pair of remote surfaces 107 and 108 are formedconcentrically about shaft 101 at the outer periphery of disc 100. Eachremote surface 107 and 108 has the above-described first and secondsurface portions, respectively, for causing light to be transmittedalong the first and second light paths. In the illustration of FIG. 6,the second light paths of the respective remote surfaces are directed todetectors 103. As best seen in FIG. 7, remote surfaces 107 and 108 arephase displaced in order to provide two-phase output signals. In FIG. 7,remote surface 107 is indicated by dotted line 107a, while remotesurface 108 is represented diagrammatically by solid line 108a The darkareas (ie, opaque areas in which the first light paths are formed by therespective remote surface portions) are represented, respectively, byhatched areas 111 and 112. The transparent areas therebetweenrespectively represent the second light paths of remote surfaces 107 and108.

It is seen that the light paths of the two remote surfaces are staggeredto form phase displaced light signals from disc 100, as will be betterunderstood by referring back to FIG. 1. The phase displacement is 90,which means that the corners of one set of remote surfaces are at themidpoint of the planar surfaces of the other remote surface. In FIG. 1,a 360 phase displacement of member is represented by movement in eitherdirection of the member from a midpoint of a second surface portion 30,as indicated by the zero degree line 115. This, of course, correspondsto a 360 phase movement in the opposite direction. A 90 movement ofmember 10 is represented by the 90 marker 116, which occurs at a comer117. At the midpoint of a first surface portion is the 180 line 118. The270 occurs at corner 119, and a complete cycle between light and dark iscompleted at the 360 point, which is the midpoint 12 of second surfaceportion 30. In the FIG. 7 illustrated embodiment, remote surface 107 canbe considered to be the one illustrated in FIG. 1. Remote surface 108has its corners between adjacent first and second surface portions atlines 115, 118, and 120 to provide the 90 phase difference in light anddark at the two remote surfaces. The utilization of a two-phasetachometer disc or displacement measuring device is quite well known.

Altemately, it may be desired to have only one set of remote surfacesextending completely around disc 100. The second set of remote surfacesmay have only one pair of first surface portions 20 to form a fiducialmark (i.e., a reference point on the rotation of disc 100). In thisinstance, the fiducial mark could be a pair of first surface portionswith a short second surface portion therebetween and bracketed by asecond surface portion extending around the periphery of disc 100. Thfiducial mark would be represented in a see-through tachon: ter disc byan opaque area or dark area followed by a shot light area which, inturn, is followed by a dark area.

FIGS. 8 and 9 are modifications, respectively, of FIGS. 4 and 5. Theaxes of rotation of the members, shown in FIGS. 8 and 9, are at withrespect to the axes of rotation in FIGS. 4 and 5. In member (FIG. 8),light-receiving surface 131 receives light from source 132. Singlecontinuous annular internal reflecting surface 133 reflects the lightreceived from source 132 in a given direction indicated by dotted line134. Remote surface 135 has first and second surface portions, as abovedescribed, for providing a second light path 136 to detector 137. Thefirst light path is along line 134, thence surface 133, back throughlight-receiving surface 131 toward source 132. The just-described membermay be mounted for rotation by affixing the member at its inner annularsurface 138 to a rotating shaft, a tubular member, or any other rotatingmember. If member 130 is to be attached on its radial surface 133, suchattachment should be either on the outer radial portion, as at 139, oron the inner radial portion, as at 140, in order to avoid making theattachment in the area of reflection of light from source 132.

In FIG. 9, there is a modification of the FIG. 5 member in which thelight-receiving surface 141 passes light from source 142 to a firstcontinuous annular reflecting surface 143. Light is transmitted radiallyoutwardly along dotted line 144 to second annular continuous reflectingsurface 145. Light is then transmitted along a given direction,indicated by line 146, to remote surface 147. Second light path 148carries light to light detector 149. The first light path (i.e., thelight reflected by first surface portions of remote surface 147) can betraced back to source 142 as described for the member 82 in FIG. 5.Support of the illustrated FIG. 9 member on a rotatable shaft can be byattachment to inner annular surface 150 without affecting the opticalproperties of the member. Altemately, annular axially facing member 151may be used to affix the FIG. 9 illustrated member to a tubular shaft orarmature. It may also be affixed to a disc without affecting the opticalproperties or operation of the annular graduated rule. Alternately, themember may be affixed on an outer facing surface 152; for example,inside a tubular armature 50, as shown in FIG. 3.

Referring next to FIG. 10, the versatility of possible combinations andvariations in the implementation of the present invention is brieflyfurther shown wherein disc-type membe" is utilized to provide twoindependent optical paths which cross and utilize a single-annularreflecting surface for effecting such configuration. Disc 160 is fixedlysecured to rotating shaft 161 for rotation therewith. It has a pair oflight receiviw surfaces 162 and 163, respectively, on a radiallyextending surface and on a circumferentially extending surface. A pairof corresponding remote surfaces 164 and 165 are formed by moldingrespectively on a circumferential surface and a radially extendingsurface. A single-annular reflective surface 166 extends concentric tothe axis of rotation of shaft 161. Source 167 supplies light throughlight-receiving surface 162, which is reflected by reflecting surface166 in a given direction indicated by dotted line 168 toward remotesurface 164. Detector 169 detects light transmitted along second path170 from remote surface 164. This is one optical system in disc 160. Asecond system is provided from source 172 through lightreceiving surface163; thence is reflected by surface 166, as at 173, along a givendirection indicated by dotted line 174 toward remote surface 165.Detector 175 detects light trans mitted along second path 176 fromremote surface 165. The two systems are independent. It should be notedthat the light paths cross at 90", as at 178. Remote surfaces 164 and165 are shaped as shown in FIG. 1. Light sources 167 and 172 anddetectors 175 and 169 are disposed outwardly of member 160 adjacentcircumferential and radial surfaces, respectively. The light source anddetector of each optical measuring system is still disposed generally onthe same sides of member 160, which facilitates good mechanical design.From inspection of FIGS. 3 10, it can be seen that the location of thedetectors and light sources and the type of light path to be providedwith the graduated rule of transparent material utilizing theconfiguration illustrated in FIG. 1 is practically unlimited.

Yet other variations are shown in FIG. 11, which the same type ofdiagrammatic illustration as FIG. 1. A member of transparent materialexhibiting internal reflection properties has light-receiving surface181. A first set of first surface portions 1&2 from a continuous darkarea indicated by hatching 183. The continuous dark area extends overthe plurality of first surface portions 182. A salient differencebetween the first surface portions 182 and the first surface portions 20of FIG. 1 is that portions 182 are constituted by a series of continuous45 surfaces. The rather sharp corners 184 between adjacent ones of saidsurface portions 182 provide a minimum of light to go therethrough. Asexplained previously, in a molded member, corners cannot be madeperfectly sharp. Each corner 184 has a finite radius as explained withrespect to FIG. 2. By setting a threshold level in a light detector, theeffect of such sharp comers can be minimized or completely eliminated.Of course, any member described herein may be fabricated by means otherthan molding to provide abrupt corners. First surface portions 182 areadjacent a short second surface portion 135. Adjacent second surfaceportion 185 is a second set of first surface portions 187 providing darkarea 186. First surface portions 187 form two complete undulations.Adjacent first surface portions 187 is another second surface portion188, which is coplanar with the first-mentioned second surface portion185. This is in contradistinction to the successively occurring secondsurface portions 30 illustrated in FIG. 1, wherein successive ones arein parallel displaced planes. To make the adjacent ones of said secondsurface portions coplanar, all that is required is that an odd number ofoutwardly facing corners 189 be formed between adjacent first surfaceportions. If an even number of corners, such as corners 184, are formed,then adjacent second surface portions will be parallel but in physicallydisplaced planes. In any event, there is provided means for making lightand dark areas on either side of optical rule 180 which minimizes thethickness thereof by providing a plurality of 45 oriented undulationswith respect to a light receiving surface 181. With this latestdescription, it should be apparent to those skilled in the art that manymore variations may be provided in the successful practice of thejust-described invention.

Another embodiment of the invention is illustrated in FIG. 12 in whichthe first light paths associated with the first surface portions do notintersect the light-receiving surface. Additionally, the first andseconeklight paths of optical graduated rule 190 leave the rule at rightangles with respect to each other. This facilitates the positioning oftwo detectors 196 and 199, respectively, in the two light paths. Bothlight detectors 196 and 199 operate at the same frequency since thefirst and second light paths contain the same frequency of lightvariations as opposed to the configuration previously described withrespect to the first light paths of the FIG. 1 and FIGS. 3- illustratedembodiments.

A pair of light sources 191 emit light, respectively, along paths 192and 193 toward optical graduated rule 190. Light traveling along path192 enters optical graduated rule 190 through light-receiving surface194 and thence is passed through the rule toward its remote surfaceconsisting of first surface portions 197 and second surface portions195. When a second surface portion 195 is aligned with light path 192,light is transmitted therethrough to light detector 196. Relativemovement of rule 190 with respect to light path 192 may align a firstsurface portion 197 therewith. Light from path 192 then reaches firstsurface portion 197 after traveling inside rule 190 to be reflected intoa first light path 198, which is at right angles to the second lightpath 1960. Accordingly, it is seen, as rule 190 moves relative to lightpath 192, detector 196 will alternately receive light and not receivelight in accordance with the displacement of rule 190.

Light traveling along path 193 is shown as impinging on first surfaceportion 197 after having traveled inside rule to b reflected along afirst light path 200 to light detector 195. Again, as rule 190 is movedrelative to path 193, light traveling along path 193 may be aligned witha second surface portion 195 to thereby permit light to traveltherethrough and not be reflected toward detector 199. Accordingly,detector 199 will alternately receive light and not receive light fromlight path 193 in accordance with the displacement of rule 190.

All first surface portions 197 are aligned in the same plane and face inthe same direction, thereby to reflect light along first light pathsparallel to the light receiving surface 194. Member 190 may be maderectilinear, as illustrated in FIG. 12, or it may be constructed as anannular member, as illustrated for the embodiments of FIGS. 3-10.

All of the illustrated embodiments have shown first surface portionsdisposed at a given 45 angle with respect to the given direction oflight travel within the optical rule, and second surface portions atother than the given 45 to permit light to leave the rule through suchsecond surface portions. Included in the scope of the present inventionare second surface portions disposed at right angles to the firstsurface portions. In the latter arrangement, light arriving at theremote surface within the graduated rule is internally reflected infirst light paths by the first surface portions extending in a firstdirection within the rule while light reflected by the second surfaceportions moves in a direction opposite to the first direction such thatlight traveling along the paths leaves the optical rule at divergentlocations to provide optical measuring properties.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What I claim is:

1. For a measurement device, a graduated optical member consisting oftransparent material with internal reflection properties having alight-receiving surface and a remote surface,

said member being capable of transmitting light from saidlight-receiving surface toward said remote surface such that said lightapproaches said remote surface in a given direction within said member,

said remote surface having a set of first planar surface portions eachdisposed substantially at 45 with respect to said given direction forreflecting in accordance with said internal reflection propertiessubstantially all light arriving along said given direction to firstlight paths, respectively substantially at right angles to said givendirection, and said first light paths leaving said member at givenlocations thereon,

said remote surface also having a set of second surface portions eachdisposed at substantially other than said giver 45 for permitting lightarriving along said given direction to follow respective second lightpaths, each said second light path leaving said transparent member atlocations other than said given locations,

said portions being alternated on said remote surface such that saidtransparent member has alternating effectively opaque andlight-transmitting portions on said first and second light paths asindicia of displacement, and

a comer joining each adjacent ones of said portions for improvingoptical demarcation therebetween.

2. The member set forth in claim 1, wherein said set of first surfaceportions is arranged in plural pairs of such surface portions facingeach other inside said member such that said first light path of eitherone of said facing surface portions has a first portion disposed atright angles to said given direction and extending between said facingfirst surface portions such that light therein is reflected by anotherone of said facing surfaces into a second portion of said first lightpath extending parallel to said given direction but with light going inan opposite direction.

3. The member of claim 2, herein said member is tubular shaped withinner and outer tubular walls, one of said surfaces being said outerwall and another of said surfaces being said inner wall.

4. The member of claim 3, wherein said first surface portions are allflat plane, smooth surfaces, said remote surface having a generalannular configuration, and said light-receiving surface being a smoothannular surface.

5. The member of claim 2, wherein said member is a unitary member havingan annular portion in which said surfaces reside and with a central axisabout which said surfaces are concentrically disposed with saidlight-receiving surface having an annular shape.

6. The member of claim 5, wherein said member is platelike with saidannular portion being a periphery of said member and all said surfacesare on the same axial side of said platelike member, and, furtherincluding an annular surface on said member disposed at 45 with respectto said light-receiving surface for reflecting light transmitted theretoinside said member from said light-receiving surface such that saidfirst direction extends outwardly of said member on the same axial sideof said member as said light receiving member is disposed.

7. The member of claim 5, further including annular internal reflectingsurface means in said annular portion optically intermediate said lightreceiving and remote surfaces for internally reflecting lighttherebetween in said given direction and along said first light path,

said member having first and second oppositely facing sides and saidannular internal reflecting surface means being included in said firstside and said light receiving and remote surfaces being included in saidsecond side, such that said first and second light paths have portionsoutside said member along said second side.

8. The member of claim 7, further including second light receiving andsecond remote surfaces, said annular internal reflecting means alsobeing optically intermediate said second light receiving and secondremote surfaces for internally reflecting light therebetween in a secondgiven direction and along a second one of first light paths, said secondone of first light paths crossing the first-mentioned first light path.

9. The member of claim 1 having plural measurement sets of said lightreceiving and remote surfaces, each said measurement set having itsrespective first set of surface portions phase translated with respectto every other first set of surface portions.

10. The member of claim 1, wherein said first and second surfaceportions, respectively, are coplanar fiat surfaces.

11. An optical system for making measurements of rotational movementsincluding,

a light source for emitting light,

a unitary rotatable member for receiving said light and consisting ofmolded transparent material exhibiting internal reflection propertiesand capable of transmitting said light,

plural planar surfaces disposed in an annulus on said member fordirecting light from said source impinging thereon from inside saidmember,

a first set of said planar surfaces disposed in spaced relationcircumferentially on said member and at 45 with respect to saidimpinging light within said member for directing same along a firstlight path,

a second set of said planar surfaces on said member for causing saidimpinging light within said member to follow a second light path andbeing intermediate said planar surfaces in said first set such thatcircumferentially alon;

said annulus there are alternate planar surfaces of said first andsecond sets for providing first and second light 5 paths whichalternately receive and don t receive light as said member is rotated,light in said first and second light paths leaving said member at spacedapart locations on said member, and

detector means operatively positioned with respect to one of said lightpaths to receive light therefrom originating at said source andresponsive to such received light to generate electrical signalsindicative of rotational movement of said member. v

12. The system of claim 11, wherein said unitary member has an annularshape with said light receiving surface being an outer circumferentialsurface thereof and said remote surface being an annular innercircumferential surface thereof, and

said light source and said detector means being on a common diameter ofsaid member radially outwardly of said light-receiving surface such thatsaid second light path extends along said common diameter intersectingsaid member adjacent said detector means.

13. The system of claim 11, wherein said unitary member has an annularinternal reflecting surface optically interposed between said lightreceiving and said remote surfaces such that both said first and secondlightpaths include portions outside said unitary member generally on thesame side thereof.

14. An optical graduated rule including transparent materi al exhibitinginternal reflection properties,

pairs of first planar surface means disposed at right angles with withrespect to each other and at 45 with respect to a given direction alongwhich light may be transmitted and being capable of reflecting lightthrough first light paths,

second planar surface means respectively interposed between adjacentones of said first planar surface means such that said means togetherconstitute a continuous rule along a first direction of alternate firstand second planar surface means,

said second planar surface means being capable of transmitting lighttherethrough in a second light path,

said first light path folding back upon itself generally in a U- shapedconfiguration, and

both said first and second light paths including a portion in saidtransparent material and portions outside said transparent material,said outside portions of said first and second light paths beingdisplaced from the other along said first direction. 15. An opticalgraduated rule consisting of transparent 5 material, the improvementincluding the combination,

a planar light-receiving surface, a remote surface having a first planarsurface portior. disposed at 45 to light entering said rule through saidreceiving surface,

a second surface portion of said remote surface disposed substantiallyat other than said 45 for transmitting light therethrough from saidreceiving surface, and

a rounded corner joining said portions such that light from saidreceiving surface is refracted to make the corner appear optically moreabrupt than the geometry of the comer.

1. For a measurement device, a graduated optical member consisting oftransparent material with internal reflection properties having alight-receiving surface and a remote surface, said member being capableof transmitting light from said lightreceiving surface toward saidremote surface such that said light approaches said remote surface in agiven direction within said member, said remote surface having a set offirst planar surface portions each disposed substantially at 45* withrespect to said given direction for reflecting in accordance with saidinternal reflection properties substantially all light arriving alongsaid given direction to first light paths, respectively, substantiallyat right angles to said given direction, and said first light pathsleaving said member at given locations thereon, said remote surface alsohaving a set of second surface portions each disposed at substantiallyother than said given 45* for permitting light arriving along said givendirection to follow respective second light paths, each said secondlight path leaving said transparent member at locations other than saidgiven locations, said portions being alternated on said remote surfacesuch that said transparent member has alternating effectively opaque andlight-transmitting portions on said first and second light paths asindicia of displacement, and a corner joining each adjacent ones of saidportions for improving optical demarcation therebetween.
 2. The memberset forth in claim 1, wherein said set of first surface portions isarranged in plural pairs of such surface portions facing each otherinside said member such that said first light path of either one of saidfacing surface portions has a first portion disposed at right angles tosaid given direction and extending between said facing first surfaceportions such that light therein is reflected by another one of saidfacing surfaces into a second portion of said first light path extendingparallel to said given direction but with light going in an oppositedirection.
 3. The member of claim 2, herein said member is tubularshaped with inner and outer tubular walls, one of said surfaces beingsaid outer wall and another of said surfaces being said inner wall. 4.The member of claim 3, wherein said first surface portions are all flatplane, smooth surfaces, said remote surface having a general annularconfiguration, and said light-receiving surface being a smooth annularsurface.
 5. The member of claim 2, wherein said member is a unitarymember having an annular portion in which said surfaces reside and witha central axis about which said surfaces are concentrically disposedwith said light-receiving surface having an annular shape.
 6. The memberof claim 5, wherein said member is platelike with said annular portionbeing a periphery of said member and all said surfaces are on the sameaxial side of said platelike member, and, further including an annularsurface on said member disposed at 45* with respect to saidlight-receiving surface for reflecting light transmitted thereto insidesaid member from said light-receiving surface such that said firstdirection extends outwardly of said member on the same axial side ofsaid member as said light receiving member is disposed.
 7. The member ofclaim 5, further including annular internal reflecting surface means insaid annular portion optically intermediate said light receiving andremote surfaces for internally reflecting light therebetween in saidgiven direction and along said first light paTh, said member havingfirst and second oppositely facing sides and said annular internalreflecting surface means being included in said first side and saidlight receiving and remote surfaces being included in said second side,such that said first and second light paths have portions outside saidmember along said second side.
 8. The member of claim 7, furtherincluding second light receiving and second remote surfaces, saidannular internal reflecting means also being optically intermediate saidsecond light receiving and second remote surfaces for internallyreflecting light therebetween in a second given direction and along asecond one of first light paths, said second one of first light pathscrossing the first-mentioned first light path.
 9. The member of claim 1having plural measurement sets of said light receiving and remotesurfaces, each said measurement set having its respective first set ofsurface portions phase translated with respect to every other first setof surface portions.
 10. The member of claim 1, wherein said first andsecond surface portions, respectively, are coplanar flat surfaces. 11.An optical system for making measurements of rotational movementsincluding, a light source for emitting light, a unitary rotatable memberfor receiving said light and consisting of molded transparent materialexhibiting internal reflection properties and capable of transmittingsaid light, plural planar surfaces disposed in an annulus on said memberfor directing light from said source impinging thereon from inside saidmember, a first set of said planar surfaces disposed in spaced relationcircumferentially on said member and at 45* with respect to saidimpinging light within said member for directing same along a firstlight path, a second set of said planar surfaces on said member forcausing said impinging light within said member to follow a second lightpath and being intermediate said planar surfaces in said first set suchthat circumferentially along said annulus there are alternate planarsurfaces of said first and second sets for providing first and secondlight paths which alternately receive and don''t receive light as saidmember is rotated, light in said first and second light paths leavingsaid member at spaced apart locations on said member, and detector meansoperatively positioned with respect to one of said light paths toreceive light therefrom originating at said source and responsive tosuch received light to generate electrical signals indicative ofrotational movement of said member.
 12. The system of claim 11, whereinsaid unitary member has an annular shape with said light receivingsurface being an outer circumferential surface thereof and said remotesurface being an annular inner circumferential surface thereof, and saidlight source and said detector means being on a common diameter of saidmember radially outwardly of said light-receiving surface such that saidsecond light path extends along said common diameter intersecting saidmember adjacent said detector means.
 13. The system of claim 11, whereinsaid unitary member has an annular internal reflecting surface opticallyinterposed between said light receiving and said remote surfaces suchthat both said first and second light paths include portions outsidesaid unitary member generally on the same side thereof.
 14. An opticalgraduated rule including transparent material exhibiting internalreflection properties, pairs of first planar surface means disposed atright angles with respect to each other and at 45* with respect to agiven direction along which light may be transmitted and being capableof reflecting light through first light paths, second planar surfacemeans respectively interposed between adjacent ones of said first planarsurface means such that said means together constitute a continuous rulealong a first direction of alternate first and second planar surfacemeaNs, said second planar surface means being capable of transmittinglight therethrough in a second light path, said first light path foldingback upon itself generally in a U-shaped configuration, and both saidfirst and second light paths including a portion in said transparentmaterial and portions outside said transparent material, said outsideportions of said first and second light paths being displaced from theother along said first direction.
 15. An optical graduated ruleconsisting of transparent material, the improvement including thecombination, a planar light-receiving surface, a remote surface having afirst planar surface portion disposed at 45* to light entering said rulethrough said receiving surface, a second surface portion of said remotesurface disposed substantially at other than said 45* for transmittinglight therethrough from said receiving surface, and a rounded cornerjoining said portions such that light from said receiving surface isrefracted to make the corner appear optically more abrupt than thegeometry of the corner.